Idle RPM

[Dano944]

My ‘83 5-spd idles at 1000-1100 rpm. Shouldn’t it idle at 850? How do I get it to idle lower? The Smog Shop said he can’t adjust the idle below where it’s at.

[wwdwgs]

Should be about 900-950, but many of us keep idle at 1000.
850 is, probably, for the Turbos.

[Dano944]

Originally Posted by wwdwgs

Should be about 900-950, but many of us keep idle at 1000.
850 is, probably, for the Turbos.

Is there a simple idle adjustment screw or is it more complicated than that?

[wwdwgs]

Yes - see this video: https://youtu.be/Yerr4jKlI1g?t=256

[walfreyydo]

https://www.clarks-garage.com/shop-manual/fuel-08.htm
https://www.clarks-garage.com/shop-manual/fuel-21.htm

[Dano944]

Thanks, but do those videos and links apply to an ‘83 944?

[wwdwgs]

video - yes: yearly 944 (with "square" dash) and late 924S (also with "square" dash) - all 4-cyl and 8-valve engines..

[Dano944]

Wwdgs…I see the idle adjustment screw imbedded in the throttle linkage. I wonder if it’s safe for me to do minor adjustments to that screw myself without doing that shorting with the wire that is shown? I guess worst case is the engine idles like crap, but then I can simply reverse the rotation?

[wwdwgs]

don't touch throttle linkage (cable), you need this (white arrow):

[Dano944]

Originally Posted by wwdwgs

don't touch throttle linkage (cable), you need this (white arrow):

Yes, I see that screw on my car. Is it safe for me to adjust that screw in/out without connecting anything else (as the video shows with a jump wire). In other words, will turning that screw allow me to easily adjust the idle to 900 rpm?

[wwdwgs]

follow Clark's instruction - there is a reason why we need to jump those two terminals.

[Monkey Wrench]

Id have a careful look about or do a smoke test because the air fuel mix particularly at idle is easily messed up by any vacuum leak. you might find a bad hose thats a little out of your view and leaking in air, then that air isn't accounted for by the ECU.. If you have issues like that Id fix them first. its a common issue because of rubber rot. Id say crankcase fumes may also make rubber not last so long.

[originalowner]

Originally Posted by Dano944

Thanks, but do those videos and links apply to an ‘83 944?

There is no idle stabilizer valve on the early car, so no port to jumper as in the video.

Early car specs from the workshop manual:

[Dano944]

Thanks for the reply. First, during a recent service at my local Porsche shop, they did a smoke test to verify any leaking vacuum tubes, and all checked out fine.
My car idles at 1000rpm, so I think I’ll just leave it as is. I just didn’t know if having a slightly high rpm would affect a smog test?

[Dano944]

One last question: Does my early 944 have a cold-start faster idle setting? My car starts and stays at 1000rpm from cold-start and never changes. I’m used to more modern cars that have a slightly faster idle on cold start, then slows down when warm.

[originalowner]

Originally Posted by Dano944

One last question: Does my early 944 have a cold-start faster idle setting? My car starts and stays at 1000rpm from cold-start and never changes. I’m used to more modern cars that have a slightly faster idle on cold start, then slows down when warm.

That probably means that your supplementary air valve is working perfectly. This valve allows extra airflow during cold start operation, and slowly closes as the engine warms up.

Your idle would be slower cold if it was not working.

[Dano944]

Originally Posted by originalowner

That probably means that your supplementary air valve is working perfectly. This valve allows extra airflow during cold start operation, and slowly closes as the engine warms up.

Your idle would be slower cold if it was not working.

So…with the supplementary valve working correctly, should the engine cold start at a higher RPM then adjust lower when the engine warms up? My car’s RPM starts and stays the same RPM all the time.

[originalowner]

I don't think there is a specification for cold idle speed. Yours is working if the car keeps running well while cold.

[Monkey Wrench]

Originally Posted by originalowner

That probably means that your supplementary air valve is working perfectly. This valve allows extra airflow during cold start operation, and slowly closes as the engine warms up.

Your idle would be slower cold if it was not working.

im wondering if it got reversed or if Im just wrong.. but doesnt the idle air valve open during operation ? if its open that would mean its running leaner due to air bypassing its "monitoring system", which is either the barn door or possibly an air mass meter, depending on year..
i would think that on a cold start you'd want it closed to make it more rich , similar to a choke would.

maybe you are referencing a different part, or quite possibly I'm wrong and just perpetually confused. ;-)

[originalowner]

It bypasses the throttle but not the afm. The dme enriches the mixture based on temperature.